To examine cardiac functions in the field of cardiovascular internal medicine, image diagnosis processes have conventionally been performed by using medical images that have been taken by employing medical image diagnostic apparatuses such as X-ray diagnostic apparatuses, X-ray Computed Tomography (CT) apparatuses, Magnetic Resonance Imaging (MRI) apparatuses, nuclear medicine diagnostic apparatuses, and ultrasonic diagnostic apparatuses.
As an example of a method for supporting such image diagnosis processes to examine cardiac functions, a method is known by which a plurality of points are set in the heart included in volume data that has been collected by a medical image diagnostic apparatus while using a predetermined time interval so that an image in which movement functions of the heart are rendered is displayed by tracking the plurality of points that have been set. As another example of image diagnosis process supporting methods, another method is known by which movement functions of the heart are analyzed by extracting images of an inner membrane and an outer membrane of the myocardia, out of an MRI image taken by using an image taking method that causes the luminance value of the myocardia to be higher than the luminance value of the lumen of the heart and another MRI image taken by using an image taking method employing a contrast agent that causes the luminance value of the lumen of the heart to be higher than the luminance value of the myocardia.
To examine cardiac functions by using X-ray transmission images that have been taken by X-ray diagnostic apparatuses, Left Ventriculography (LVG) processes are commonly performed. An LVG process is performed so as to take an X-ray transmission image in which the myocardium of the left ventricle is opacified by injecting a contrast agent through an LVG-purpose pig tail catheter inserted into the left ventricle of the heart. When X-ray transmission images have sequentially been taken by performing such an LVG process, medical doctors are able to make a diagnosis regarding, for example, degradation of the movement functions of the heart by referring to the images rendering the manner in which the myocardial tissue moves. Further, by calculating an Ejection Fraction (EF) value of the left ventricle, based on an X-ray transmission image that has been taken by performing an LVG process, medical doctors are able to quantitatively analyze movement functions of the heart.
Generally speaking, to examine cardiac functions by using X-ray diagnostic apparatuses, a diagnosis regarding vessel stenosis or the like is made first by taking an X-ray transmission image through a coronary angiography process, before a further diagnosis is made by performing an LVG process.
To perform the LVG process described above, for example, 30 milliliters of contrast agent is injected for performing one LVG image taking process, because it is necessary to take an image of the inside of the left ventricle without missing any part thereof. In contrast, the amount of contrast agent that is required to perform a coronary angiography process is 6 milliliters to 15 milliliters. As understood from the above, a large amount of contrast agent needs to be injected to perform an LVG process. In addition, to avoid laying a burden on the functions of the kidney, an upper limit is set for the amount of contrast agent that can be injected into an examined subject during one examination process. Thus, it is difficult to repeatedly perform the LVG process a plurality of times, because a large amount of contrast agent needs to be injected.
Further, the image-taking time period required to perform a coronary angiography process is about 5 seconds. In contrast, the image-taking time period required to perform an LVG process is longer (e.g., about 10 seconds to 20 seconds). Thus, the X-ray exposure amount during an LVG process is larger. In addition, an LVG process requires the use of a dedicated catheter as explained above. For this reason, in the case where an LVG process is performed after a coronary angiography process is performed, it is necessary to insert an LVG-purpose catheter into an examined subject after a coronary-angiography-purpose catheter has been removed. Thus, it takes a longer period of time to perform the examination.
As explained above, analyzing movement functions of the heart by using X-ray transmission images that have been taken through an LVG process has a problem where a burden is laid on the examined subject.